A conventional shopping trolley as shown in FIGS. 5, 6 may be used to load foods, vegetables, and other daily commodities when buying somethings from a supermarket or shopping center, having a pair of rear wheels 3 and a pair of front wheels 5 rotatably mounted to a basket 1 and a handle 4 pivotally secured to the upper bars of the basket 1 by pivots 40. When using such a conventional trolley for climbing a staircase S as shown in FIG. 6, the front wheels 5 is separated from the rear wheels 3, unstably rested on the staircase S and the gravity center W when loaded by heavy materials in the basket 1 will be moved outwardly, possibly causing an outwardly deviating gravity center W of the trolley and possibly causing a rearwardly collapse of the trolley carrying person, especially dangerous for a weak old woman, when climbing a staircase.
Even though the basket 1 may be folded as shown in dotted line of FIG. 6 to move the gravity center rearwardly, the materials such as foods stored in the basket 1 may however be compressed, squeezed, or even damaged or broken.
It is therefore expected to disclose a safer trolley climbable on a staircase.